It is well known that cap ply reinforcements spirally wound on the belt package with 0° to 5° to the equatorial plane of the tire improves performance and high speed durability of the tire. Nylon 6.6 has been using widely for several years as cap ply due to its high restraining force at high speed conditions, preventing or reducing tire growth and belt edge separations.
In U.S. Pat. No. 4,284,117, belted pneumatic tires characterized by improved tread reinforcing breaker constructions are disclosed. In such applications, the cap ply is disposed directly on the radially outermost belt ply of the tire. Since the cap ply is formed from single twisted yarns rather than cords, the cap ply is thinner than conventional cap plies, has superior flexibility and heat dissipation characteristics. The textile yarns are oriented at a 0° angle to the median equatorial plane of the tire. In this patent exists no information about material properties.
In U.S. Pat. No. 3,849,976 high strength, high modulus and low heat shrinkage nylon 66 cord has been disclosed as tire reinforcement. In such applications nylon 6.6 cord has L5 modulus higher than 60 g/d.100% (54 g/dtex.100%). But such cords have relatively low heat shrinkage (less than 4%) to generate sufficient shrink force to compensate the modulus-drop of the cap ply cord at high speed temperatures of the crown area in the tire and too stiff for sufficient bending fatigue resistance.
In U.S. Pat. No. 3,850,219 and U.S. Pat. No. 3,960,628 nylon cap ply has been mentioned, but no information on tensile and thermal properties of the cord is given.
In U.S. Pat. No. 5,115,853 low-denier (420 dx2) nylon cords having maximum 7 tpi (276 tpm) twist have been disclosed as cap ply. The cap ply(overlay) cord have an elongation at break of 15% to 20%. The heat shrinkage properties of the cap ply cords are not mentioned. In U.S. Pat. No. 5,908,520 and U.S. Pat. No. 6,609,552 single twisted nylon 66 yarns have been disclosed as cap ply in tire.